Position sensor

ABSTRACT

We describe a position sensor comprising drive electronics to drive a first tuned resonant circuit at a resonant frequency, a moveable mechanical control associated with a second, passive tuned resonant circuit and read-out electronics coupled to the first tuned resonant circuit to sense a position of the control. A first frequency of resonance of the first tuned resonant circuit matches a second frequency of resonance of the second, passive tuned circuit, and the first and second frequency resonance match a resonant frequency of the drive signal. The first tuned resonant circuit has an input coupled to the drive electronics, an output coupled to the read-out electronics and a resonant LC circuit coupled in series between the input and output. The variable output signal is dependent on an amplitude of a signal at the output of the first tuned resonant circuit.

RELATED APPLICATIONS

This application is a divisional application of U.S. patent applicationSer. No. 13/596,635, filed 28 Aug. 2012, which is incorporated herein inits entirety.

FIELD OF THE INVENTION

We describe inductive position sensors with applications in musicalinstrument control and other fields.

BACKGROUND

Musicians often use electronic effects to modify the sound of theirinstrument during composition and recording and during liveperformances. For many of these effects it is desirable for the musicianto be able to control an aspect of the effect and this is typicallyachieved by interaction with controllers such as linear sliders, alsoknown as faders, rotary knobs or foot pedals, also known as expressionpedals. These controllers permit a musical effect to be variedcontinuously between a maximum and a minimum of that effect.

Using the example of the expression pedal, the effect of the expressionpedal on the musical sound varies as the musician presses the pedal. Thepedal is thus the controller that the musician uses to apply the desiredamount of the effect to the sound. Different expression pedals existsuch as volume pedals where the sound level is modified, wah-wah pedalswhere the frequency characteristics of the sound is modified and genericcontroller pedals where a control signal is used, for example, to adjusta parameter of a synthesizer. All of these pedals have in common theneed to know how much the pedal has been pressed by the musician so thatthis can be converted into application of the correct amount of theeffect being controlled by the pedal.

Other controllers, such as faders and knobs, use a similar principle tothat described for the expression pedal. For a fader, the amount of theeffect to be applied to the sound is determined by how much the faderhas been moved. For a knob, the amount of the effect to be applied tothe sound is determined by how far the knob has been rotated.

It is also possible to control a musical effect by using a controllerwhich does not require the musician to touch it. For example,non-contact optical controllers can detect the proximity of an objectsuch as the musician's hand as is described in U.S. Pat. No. 6,153,822or foot as is described in U.S. 2006/0278068 A1.

All of these controllers have in common the fact that the control of theeffect is via the separation of a fixed reference element and a moveableelement (such as pedal, slider, knob, ring), the position of which ischosen by the musician to achieve the desired musical effect.

The control of the musical effect can be accomplished in two ways:direct and indirect. Direct control of the effect is where the movementof the moveable element causes direct variation of a circuit element inan electronic circuit. Direct control therefore requires a circuitelement whose electrical response can be varied by the movement of saidmoveable element. Indirect control of the effect is where the positionof said moveable element with respect to said fixed reference element ismeasured to give a value of the mutual separation between said elementsand this mutual separation value is used to control a separate circuitelement in an electronic circuit or is used as an input parameter to adigital signal processing algorithm. It is therefore a requirement forindirect control to measure accurately the mutual separation of saidfixed reference element and said moveable element.

Volume control pedals and wah-wah pedals have characteristically usedpotentiometers as a direct means of controlling the sound effect, suchas is described in U.S. Pat. No. 3,530,224. A significant problemassociated with this use of potentiometers is that most potentiometersare not designed for the large number of operating cycles required insuch controllers, and those that are very expensive. As potentiometerswear out, the reproducibility of the control is compromised and noisecan be introduced into the corresponding electronic circuits. Indeed itis common to need to replace the potentiometers in wah-wah and volumecontrol pedals when they wear out. It is therefore highly desirable tohave an alternative solution that is robust and does not suffer fromwear during operation.

Optical position sensing can be used as an alternative topotentiometers, for example as is described in U.S. Pat. No. 6,859,541B1, but the performance of such systems is vulnerable to degradation bycontamination and they need to be cleaned to retain optimal performance.Moreover, they can contain delicate optical elements such as shades orfilms with graduated transparency which make then sensitive to shock andvibration with a corresponding reduction in long-term reliability. Theycan also be more expensive than potentiometers. It is thereforedesirable to have an alternative position sensor that is unaffected bydirt and moisture contamination and is robust to shock and vibrationsuch as is experienced during normal use.

Magnetic sensors such as Hall probes where a permanent magnet is movedwith respect to the Hall probe are another alternative to potentiometersthat is sometimes used. The inventors hereof have found that Hall probesthat are able to detect precise variations in a magnetic field, such ascaused by the movement of a proximate permanent magnet, are expensiveand require operating voltages higher than is commonly used for amicrocontroller-based musical effect. Hall probes can also be sensitiveto other nearby magnetic fields which is a problem when multiplecontrollers are being used in proximity to one another. Moreover,magnetic sensors which detect the proximity of a permanent magnet canonly be used in indirect control schemes. In electronic musicalinstrument applications, an alternative low-voltage, accurate andinexpensive position sensor that has the flexibility to be used in bothdirect and indirect control schemes is highly desirable.

Inductive proximity sensors show promise as an alternative topotentiometers. However, they are not currently used in the electronicmusical industry because those that are commercially available areexpensive and have technical limitations in this field of application.Commercially available inductive proximity sensors use an inductive coiland a ferrite core material to detect the presence of a nearby metallicobject and this metallic object needs to be close to the inductive coilfor accurate position measurements to be made, or the inductive coilneeds to be prohibitively large. Moreover, this type of inductiveproximity sensor will interact with others of the same type if usednearby because of their sensitivity to metallic objects; the metallicobjects from the different sensors cannot be measured independently.Current inductive proximity sensors are clearly not suitable for use inelectronic musical instrument applications, and an alternative solutionis required.

We will describe a solution that improves the robustness of thecontroller so that it is substantially unaffected by dirt and moisturecontamination, is not affected by the levels of shock and vibrationexperienced during normal use and does not wear out, that is accurate,that is inexpensive and that can be manufactured reliably andreproducibly. For maximum flexibility the new solution needs to becapable of providing accurate position sensing over a range ofdistances, and be capable of being operated in a multi-sensorenvironment.

Background prior art can be found in GB2,320,125A; U.S. Pat. No.4,580,478 and U.S. Pat. No. 4,838,139. Each of these documents describesan arrangement in which the inductance of the active coil is changed toprovide a corresponding change in resonant frequency, which is thendetected. WO2011/128698 was published after the priority date of thepresent application, albeit it has an earlier priority date. U.S.2002/0140419, teaches the use of a particular circuit configuration inwhich the transmitted and received magnetic fields may have the samefrequency, teaching the skilled person to employ ‘anti-dazzle means’ todistinguish between the transmitted and received fields. It is desirableto improve upon this approach.

SUMMARY OF THE INVENTION

According to a first aspect of the invention there is therefore provideda musical effect device having an input to receive an input signal froman electric or electronic musical instrument or microphone, an output toprovide an output signal comprising modified version of said inputsignal, and an effect control circuit coupled between said input andsaid output to apply a controllable effect to said input signal toprovide said output signal, wherein said effect control circuit has acontrol connection to control a level of said controllable effectapplied to said input signal; and wherein said musical effect devicefurther comprises a moveable mechanical control and a position sensorhaving an output coupled to said control connection, to sense a positionof said moveable mechanical control, wherein said position sensorcomprises: a first tuned resonant circuit; drive electronics coupled tosaid tuned resonant circuit to drive said first tuned resonant circuitwith a drive signal at a resonant frequency; a second, passive tunedresonant circuit associated with said moveable mechanical control,wherein said electrically reactive element provides a variablemodification to a response of said first tuned resonant circuitdependent on a relative position of said second, passive tuned resonantcircuit with respect to first tuned resonant circuit; and read-outelectronics coupled to said first tuned resonant circuit, to provide avariable output signal responsive to said relative position of saidsecond, passive tuned resonant circuit with respect to first tunedresonant circuit, wherein said variable output signal of said read-outelectronics provides said position sensor output coupled to said controlconnection of said effect control circuit; wherein a first frequency ofresonance of said first tuned resonant circuit matches a secondfrequency of resonance of said second, passive tuned circuit, andwherein said first and second frequency resonance match said resonantfrequency of said drive signal; wherein said first tuned resonantcircuit comprises an input coupled to said drive electronics, an outputcoupled to said read-out electronics and a resonant LC circuit coupledin series between said input and said output; and wherein said variableoutput signal is dependent on an amplitude of a signal at said output ofsaid first tuned resonant circuit.

Embodiments of the above described arrangement provide a number ofadvantages and, in particular, simplify interfacing with amicrocontroller, are more easily incorporated into a musical effectsdevice, and can provide increased sensitivity in such applications.

In some preferred embodiments the first tuned resonant circuit comprisesan input resistor and an inductor coupled in series between the inputand output of a circuit and first and second capacitors coupled inparallel between the series inductor and the common connection betweenthe input and output, in particular one coupled to either end of theinductor. This helps to increase sensitivity.

Embodiments of the circuit operate by providing a controllable amplitudesignal dependent on the mutual separation of the active and passivetuned circuits. To achieve this the resonant frequencies of the activeand passive tuned circuits should be matched to one another and also tothe drive frequency. In practice, however, in particular in a musicaleffects device, the tuning of these resonant circuits may be affected bya metal component on or adjacent which one or both of the first andsecond resonant circuits is mounted. This has the effect of de-tuningone or both of these circuits. Although this may be addressed to someextent by spacing an inductor of the relevant tuned circuit away fromthe metal component, improved techniques are desirable and inembodiments the capacitance of one or both resonant circuits is selectedso that the de-tuned resonant frequencies of the or each circuit matchesboth the other circuit and the drive frequency. In embodiments the drivesignal is generated by a microprocessor and the frequency may varyslightly with microprocessor timing and thus in embodiments the optimumcapacitance values may be determined by a combination of calculationsand experiment, for example for a particular manufactured device.

Interestingly in this context the inventor has determined that once thede-tuned frequencies are matched there is no substantial furtherde-tuning by relative movement of the tuned circuits with respect to oneanother. More particularly, when the de-tuned frequencies are matchedthe output of the active tuned circuit has a substantially constantphase offset with respect to the drive signal, and this in turnfacilitates the use of sensitive synchronous detection techniques todetermine the relative position of the two tuned circuits, even wherethe circuits are de-tuned by adjacent electrically conducting elements.It is, nonetheless, still preferable to provide an electricallynon-conductive region between the coil of the or each resonant circuitand an adjacent metallic/conducting element on or adjacent which thecoil is mounted.

In a related aspect the invention provides a method of controlling amusical effects device, the method comprising: providing the device witha moveable control; providing a second passive tuned resonant circuitfor said moveable control; and sensing a position of said moveablecontrol using a driven first tuned resonant circuit and read-outelectronics coupled to said driven tuned resonant circuit to sense arelative position of said first and second tuned resonant circuits;wherein said sensing comprises: driving said first tuned resonantcircuit, with a drive signal at a resonant frequency, at an input ofsaid first tuned resonant circuit; providing a resonant LC circuitcoupled in series between said input and an output of said first tunedresonant circuit; matching a first frequency of resonance of said firsttuned resonant circuit with a second frequency of resonance of saidsecond, passive tuned circuit and with said resonant frequency of saiddrive signal; and controlling said musical effects device using anamplitude of a signal at said output of said first tuned resonantcircuit.

As previously mentioned, in embodiments a variable output signal may begenerated by synchronous demodulation of an output of the first resonantcircuit, synchronising to the drive signal. In other embodiments,however, direct control of the musical signal may be employed bymodulating an audio signal onto the drive signal for the first tunedresonant circuit and afterwards recovering this by demodulation. Theamplitude of this audio signal is then directly affected by theproximity of the second tuned resonant circuit, which may be used tocontrol the amplitude of or other effects applied to the musical signal.

According to another aspect of the invention there is therefore provideda musical effect device having an input to receive an input signal froman electric or electronic musical instrument or microphone, an output toprovide an output signal comprising modified version of said inputsignal, and an effect control circuit coupled between said input andsaid output to apply a controllable effect to said input signal toprovide said output signal, wherein said effect control circuit has acontrol connection to control a level of said controllable effectapplied to said input signal; and wherein said musical effect devicefurther comprises a moveable mechanical control and a position sensorhaving an output coupled to said control connection, to sense a positionof said moveable mechanical control, wherein said position sensorcomprises: first a tuned resonant circuit; drive electronics coupled tosaid tuned resonant circuit to drive said first tuned resonant circuitat a resonant frequency; an electrically reactive element associatedwith said moveable mechanical control, wherein said electricallyreactive element provides a variable modification to a response of saidfirst tuned resonant circuit dependent on a relative position of saidelectrically reactive element with respect to first tuned resonantcircuit; and read-out electronics coupled to one or both of said firsttuned resonant circuit and said electrically reactive element, toprovide a variable output signal responsive to said relative position ofsaid electrically reactive element with respect to first tuned resonantcircuit, wherein said variable output signal of said read-outelectronics provides said position sensor output coupled to said controlconnection of said effect control circuit.

The above described technique has been found to be particularly reliableand effective. Preferably, but not essentially, the electricallyreactive element comprises a second tuned resonant circuit tuned to afrequency at which the first tuned resonant circuit is driven.Optionally multiple first and second tuned resonant circuits may beemployed, each operating at a different respective frequency, to providea plurality of respective control parameters for one or more musicaleffects.

A particularly advantageous coil arrangement has been found to be a flator planar coil defined by tracks on a printed circuit board, as thishelps achieve a well defined, repeatable geometry. The flat spatialconfiguration is also advantageous, particularly for a foot pedal typedevice, when one coil may be mounted on the base and a second on thefoot plate. Where the foot plate is metal the coil may be slightlyspaced away from the foot plate, to reduce de-tuning, but this is notessential. In embodiments the foot plate incorporates a stop, forexample opposite a hinge at one end of the foot plate, to inhibit thecoils of the first and second tuned circuits from touching when the footplate is fully depressed.

In another embodiment the moveable mechanical control is a wearablecontrol, to provide additional scope for musical effect modification.For example the moveable mechanical control may comprise a wrist band orstrap on which is attached the second tuned resonant circuit. Inembodiments the coil of the second tuned resonant circuit is smaller (asa smaller lateral extent) than that of the first tuned circuit, whichmay be mounted on the instrument. This helps to achieve increased rangeand reliable operation.

In a related aspect the invention provides a method of controlling amusical effects device, the method comprising: providing the device witha moveable control; providing an electrically reactive element for saidmoveable control; sensing a position of said moveable control using adriven tuned resonant circuit and read-out electronics coupled to one orboth of said electrically reactive circuit and said tuned resonantcircuit to sense a relative position of said moveable control and saidtuned resonant circuit by sensing a signal from said driven tunedcircuit; and controlling said musical effects device using said positionsensing.

The invention also provides a position sensor comprising an active tunedresonant circuit, providing a signal which varies as the mutualseparation of said active tuned resonant circuit and an electricallyreactive element is varied, drive electronics connected to said activetuned resonant circuit and read-out electronics connected to either saidactive tuned resonant circuit or said electrically reactive element.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects of the invention will now be described indetail, with reference to the accompanying drawings, in which:

FIG. 1 shows an active tuned resonant circuit according to the presentinvention.

FIG. 2A shows a passive tuned resonant circuit according to the presentinvention and FIG. 2B shows a passive tuned resonant circuit connectedto the read-out electronics.

FIGS. 3A, 3B and 3C show linear, angular and translational relativemovement respectively between the inductive coil of the active tunedresonant circuit and the electrically reactive element which can bedetected according to the present invention.

FIG. 4 shows an example of a simple read-out electronic circuitcomprising a synchronous demodulator which may be used by the presentinvention.

FIG. 5 shows a cross section view of a foot-pedal wherein the positionof the foot-pedal is determined using the present invention.

FIG. 6 shows a cross section view of a slider control wherein theposition of the slider is determined using the present invention.

FIG. 7 shows a musician playing a musical instrument wherein saidmusician is wearing the electrically reactive element and said musicalinstrument incorporates the active tuned resonant circuit according tothe present invention.

FIG. 8 shows a cross section view of non-conductive elements interposedbetween the inductive coils and electrically conductive elements, suchas elements of an enclosure, according to embodiments of the presentinvention.

FIG. 9 shows a block diagram of a first embodiment of a musical effectsdevice according to the invention.

FIG. 10 shows a block diagram of a second embodiment of a musicaleffects device according to the invention.

FIG. 11 shows a block diagram of a third embodiment of a musical effectsdevice according to the invention.

FIGS. 12 a and 12 b illustrate an example calibration procedure for themusical effects devices of FIGS. 9 to 11 and the application of thecalibration procedure.

DESCRIPTION OF PREFERRED EMBODIMENTS

A preferred embodiment comprises an active tuned resonant circuit 29, asshown in FIG. 1 inductively coupled to an electrically reactive element20, as shown in FIG. 3, henceforth referred to as the reactive element.This provides a signal which varies as the mutual separation of saidactive tuned resonant circuit and said reactive element is varied, amechanism or housing which enables the mutual separation of said activetuned resonant circuit and said reactive element to be varied, driveelectronics connected to said active tuned resonant circuit and read-outelectronics connected to either said active tuned resonant circuit or tosaid reactive element.

The active tuned resonant circuit FIG. 1 comprises an input resistor 4,an inductive coil 1, two capacitive elements 2 and 3, a means ofconnecting 5 drive electronics to the input resistor 4 and a means ofconnecting 7 read-out electronics to the read-out point 6. The inputresistor 4 may be omitted, but it is preferred because it performs twouseful functions: it limits the current supplied to said active tunedresonant circuit from said drive electronics which reduces the operatingcurrent required and thus reduces both power consumption andelectro-magnetic emissions from said active tuned resonant circuit; andincreases the sensitivity of proximity detection when the read-outelectronics are connected to said active tuned resonant circuit. Theinductive coil 1 provides a means of coupling between said active tunedresonant circuit and the reactive element. The capacitive elements 2 and3 together with the inductive coil 1 form a resonant LC circuit. Thetotal value of the capacitance can be adjusted to tune the frequency ofresonance of said active tuned resonant circuit. In the case where saidinput resistor 4 is not used, only one capacitive element 3 is required.

Referring to FIG. 2, the reactive element preferably comprises a passivetuned resonant circuit which comprises an inductive coil 8, a capacitiveelement 9 and optionally a means of connecting 11 read-out electronicsto the read-out point 10. In the case where said read-out electronicsare connected to the active tuned resonant circuit FIG. 1 said inductivecoil 8 and capacitive element 9 are connected to form a closed resonantLC circuit FIG. 2A. The value of the capacitance of said capacitiveelement 9 is preferably chosen to tune the frequency of resonance ofsaid passive tuned resonant circuit to match that of said active tunedresonant circuit FIG. 1. When said passive and active circuits are thustuned, it is possible to operate in close proximity a plurality ofsensors according to the present invention which can be used, forexample, to simultaneously measure different axes of motion such as butnot limited to horizontal, vertical and rotational.

The reactive element may alternatively comprise an electricallyconductive object when the read-out electronics are connected to theactive tuned resonant circuit 7 in FIG. 1. However, the range of mutualseparation of the active tuned circuit and the electrically conductiveobject over which an accurate position measurement can be made is lowerthan when a passive tuned resonant circuit FIG. 2 is used.

The inductive coils used in the active tuned resonant circuit 1 and thepassive tuned resonant circuit 8 can be of any type. However usingplanar spiral coils formed by tracks on a printed circuit board hasthree main advantages: they are inexpensive, they can be made withhighly reproducible values of inductance and the printed circuit boardcan also be used to mount the other components required, namely thecapacitive elements 2, 3 and 9. It is therefore possible to design twoinductive coils whose inductance values are closely matched. In thiscase, one such inductive coil can be used in said active tuned resonantcircuit FIG. 1, and another similar inductive coil used in said passivetuned resonant circuit FIG. 2. When such matched inductive coils areused said active and passive circuits can be tuned by matching thecapacitance of the capacitive element 9 (Cp) in said passive tunedcircuit FIG. 2 with the capacitance of the series combination of the twocapacitive elements 2 (Ca1) and 3 (Ca2) in said active tuned resonantcircuit FIG. 1, thus: Cp=1/((1/Ca1)+(1/Ca2)).

The inventors have found that optimal performance, where the sensitivityof position sensing and the distance over which position sensing ispossible are both maximised, is achieved when the frequency of resonanceof the passive tuned circuit is as close as possible to the frequency ofresonance of the active tuned resonant circuit. In this case, thefrequency of resonance of said active tuned resonant circuit does notchange substantially when the mutual separation of said active tunedresonant circuit and said passive tuned resonant circuit is varied whichin turn means that the corresponding signal at the read-out point 6 or10 retains a constant phase offset with respect to the phase of thesignal from the drive electronics thus ensuring a maximal response fromthe read-out electronics when using phase-sensitive detection methods.Indeed it is possible to use this phenomenon to aid the tuning of saidpassive resonant circuit: by observing the relative phase of said signalfrom said drive electronics and said signal at said read-out point, thevalues of the capacitive element Cp can be adjusted until said relativephase does not change substantially when said mutual separation isvaried.

When the inductive coil 1 or 8 is placed close to a metallic or otherelectrically conductive element, such as an enclosure, the effectivevalue of inductance of said coil is changed causing a correspondingchange in the frequency of resonance of the active tuned resonantcircuit or of the passive tuned resonant circuit, a phenomenon hereinreferred to as detuning. Such detuning can be compensated for in twoways. Firstly, referring to FIG. 8, a non-conductive element 22, such asbut not limited to an air-gap or plastic spacer, can be interposedbetween said inductive coil 1 and said electrically conductive element24 to reduce the amount of detuning of said active tuned resonantcircuit. Similarly, a non-conductive element 23, can be interposedbetween said inductive coil 8 and said electrically conductive element25 to reduce the amount of detuning of said passive tuned resonantcircuit. Preferably the thickness of said non-conductive elements 22 and23, and thus the separation of said inductive coils 1 and 8 from saidconductive elements 24 and 25, shall be the same. In this way, detuningis matched and the detuned frequency of resonance of said active tunedresonant circuit will match the detuned frequency of resonance of saidpassive tuned resonant circuit. Secondly, the frequency of resonance ofeither or both of said active tuned resonant circuit and said passivetuned resonant circuit can be changed by changing the value ofcapacitance of one or more of the capacitive elements 2, 3 and 9 suchthat the detuned frequency of resonance of said active tuned resonantcircuit matches the detuned frequency of resonance of said passive tunedresonant circuit.

It is preferred that in such cases said detuning does not change whenthe mutual separation of said active and said passive elements ischanged thus ensuring that the frequency of resonance of said active andsaid passive elements does not change. This can be achieved by arrangingfor the frequency of resonance of the passive tuned circuit tosubstantially match the frequency of resonance of the active tunedresonant circuit.

The drive electronics comprise a means of generating an oscillatingvoltage drive waveform at a frequency equal to or close to the resonantfrequency of the active tuned resonant circuit. Typically, but by way ofnon-limiting example, this waveform is a square waveform generated bythe output of a microcontroller timer or a digital or analogue timingcircuit.

The read-out electronics comprise a means of generating a low-frequencyor DC voltage proportional to the amplitude of the signal at theread-out point 6 or 10. Typically, but by way of non-limiting example,this comprises a synchronous demodulator (phase sensitive detector)circuit 30 as shown in FIG. 4. The signal from said read-out point isconnected to 22 and demodulated by an analogue switch 25 controlled bythe oscillating voltage drive waveform connected to 23 whose phase isoptionally adjusted by a phase shifting element 24 and a low-frequency(or dc) voltage is presented at 28 by a low-pass filter comprising aresistor 26 and a capacitive element 27. Alternative read-out electroniccircuits may comprise phase-sensitive rectifiers, phase-insensitiverectifiers, and non-synchronous demodulators as understood by thosetrained in the art.

When used to indirectly control the musical signal, the low-frequencyoutput voltage from the read-out electronics can be used to control aseparate circuit element in an electronic circuit or converted to adigital value via an analogue-to-digital-converter and used as an inputparameter to a digital signal processing algorithm or transmitted asmusical instrument digital interface (MIDI) messages.

In the case where the present invention is used to directly control themusical signal, the drive waveform can be modulated by the musicalsignal, and said musical signal recovered by demodulation in theread-out electronics. The amplitude of the recovered signal thus dependsdirectly on the mutual separation of the inductive coil of the activetuned resonant circuit 1 and the reactive element 20, thus an embodimentof the invention can itself be a circuit element in an electronicmusical effect circuit.

In the case where the reactive element is a passive tuned resonantcircuit FIG. 2, the active tuned resonant circuit FIG. 1 is inductivelycoupled to said passive tuned resonant circuit. The strength of theinductive coupling increases as the mutual separation of the centre ofthe two inductive coils 1 and 8 which are elements of said circuits isdecreased. There is no requirement for said inductive coils to come intocontact with one another, thus eliminating any mechanical wear, thusimproving robustness and reliability.

The means of operation of the inductive coupling depends on theconfiguration of the passive tuned resonant circuit FIG. 2. In the casewhere said passive tuned resonant circuit is connected to the read-outelectronics FIG. 2B, the oscillating current in the inductive coil 1 ofthe active tuned resonant circuit FIG. 1 induces a corresponding currentin the inductive coil 8 of said passive tuned resonant circuit whichallows a voltage to be measured by said read-out electronics. In thecase where said active tuned resonant circuit is connected to saidread-out electronics and said passive tuned resonant circuit forms aclosed resonant LC circuit FIG. 2A, the oscillating current in theinductive coil 1 of said active tuned resonant circuit induces acorresponding current in said inductive coil 8 of said passive tunedresonant circuit and because said passive tuned resonant circuit is aclosed circuit this current is dissipated by the resistance of saidinductive coil 8. Energy is thus transferred from said inductive coil 1in said active tuned resonant circuit FIG. 1 to said inductive coil 8 insaid passive tuned resonant circuit FIG. 2A. A consequence of thisenergy transfer is that the amount of energy that can be stored in saidactive tuned resonant circuit FIG. 1 is decreased as the mutualseparation of said passive tuned resonant circuit and said active tunedresonant circuit is decreased. This decrease in stored energy in theactive resonant circuit can be measured by the read-out electronics as adecrease in the voltage amplitude at the read-out point 6.

In the case where the reactive element is an electrically conductiveobject, the magnetic field generated by the active tuned resonantcircuit FIG. 1 induces an eddy current in said electrically conductiveobject. Thus energy is transferred from said active tuned resonantcircuit to said electrically conductive object, causing a reduction inthe amount of energy that can be stored in said active tuned resonantcircuit when the mutual separation of said electrically conductiveobject and said active tuned resonant circuit is decreased. However, fora given mutual separation of said active tuned resonant circuit and saidreactive element, the amount of energy that is transferred in this caseis lower than in the case where the reactive element is a passive tunedresonant circuit FIG. 2.

The mechanism or housing which facilitates the variable separation ofthe inductive coil 1 of the active tuned resonant circuit and thereactive element 20 can support different methods of movement: linearFIG. 3A, angular FIG. 3B, translational FIG. 3C, or a combination ofthese. Thus possible mechanisms and housings include but are not limitedto: a foot pedal FIG. 5, a slider FIG. 6 and a musician moving saidactive tuned resonant circuit or said reactive element FIG. 7.

Such a mechanism or housing typically includes a fixed element and amoveable element. It such cases is preferable for the fixed element tocontain the active tuned resonant circuit FIG. 1 to which the read-outelectronics are connected, and for the moveable element to contain thereactive element 20. In this configuration no electrical connections arerequired to said moveable element thus improving robustness andreliability. Furthermore, this configuration allows the electroniccircuits to be fully enclosed inside a non-conductive housing to furtherimprove the reliability of the entire musical effect electroniccircuits. However, it is also possible for the mechanism or housing toinclude two moveable elements. In such cases there is no preference forthe location of said active tuned resonant circuit and said reactiveelement.

Referring to FIG. 5, a foot-pedal may comprise a fixed base-plate 12, amoveable foot-plate 13 connected to said base-plate via a hingemechanism 14 to facilitate controlled variation of the mutual angularseparation FIG. 3B of said base-plate and said foot-plate. In such afoot-pedal, the reactive element 20 can be located in said foot-plateand the inductive coil 1 of the active tuned resonant circuit can belocated in said base-plate. An end-stop element 26 maintains a minimumseparation between said inductive coil 1 and said reactive element 20 toprevent contact thereof, thus improving robustness and reliability. Inthe case where said base-plate comprises an electrically conductivematerial, an air gap or spacer 22 comprised of a non-conductive materialis interposed between said inductive coil 1 and said base-plate. In thecase where said foot-plate comprises an electrically conductivematerial, an air gap or spacer 23 comprised of a non-conductive materialis interposed between said reactive element 20 and said base-plate 13.When the read-out electronics are connected to said active tunedresonant circuit, there are no electrical connections required to bemade to the reactive element 20 thus no electrical connection isrequired to movable parts thus further improving robustness andreliability.

Referring to FIG. 6, a linear slider mechanism may comprise a fixedhousing 15 and a moveable slider knob 16 moving along a track in saidfixed housing wherein the mutual translational separation FIG. 3C ofsaid fixed housing 15 and said moveable slider knob 16 can be varied assaid slider knob 16 moves back and forth along its track. In such aslider mechanism, the reactive element 20 can be mounted on saidmoveable slider knob 16 and the inductive coil 1 of the active tunedresonant circuit can be located in said fixed housing 15. When theread-out electronics are connected to said active tuned resonantcircuit, there are no electrical connections required to be made to thereactive element 20 thus no electrical connection is required to movableparts thus improving robustness and reliability.

Referring to FIG. 7, a musician may vary their position relative to amusical instrument and it is desirable to use the musician's movement asa means of controlling the sound from the musical instrument. In thiscase, the inductive coil 1 of the active tuned resonant circuit can belocated in an electronic component or musical instrument 17 that formspart of the electronic musical instrument environment used by themusician and the reactive element 20 can be located in a moveableelement 18 that the musician holds or wears such as, by way ofnon-limiting examples, jewelry, a musical instrument, a baton orclothing. Because there need be no electrical connections to saidreactive element 20 the moveable element 18 can be moved freely by themusician. Furthermore, in the case of said reactive element comprising apassive tuned resonant circuit FIG. 2A whose frequency of resonance istuned to match that of said active tuned resonant circuit, multiple setsof active tuned resonant circuits and passive tuned resonant circuitscan be combined when each set is tuned to operate at a resonantfrequency different from the other sets. In this case it is possible fora musician to independently control different aspects of theirperformance by varying the positions of each reactive elementindependently.

FIG. 9 shows a block diagram of a first embodiment of a musical effectsdevice 100 according to the invention. In this embodiment a drivewaveform 31 such as a square or rectangular waveform is produced by, forexample, a microcontroller or other processor and provided to an input 5of an active circuit 29 of the type shown in FIG. 1. The driver waveformis also provided to input 23 of the phase sensitive detector block 30 ofFIG. 4. The output 7 of the active circuit 29 provides a second input tothe phase sensitive detector block 30, which has an output 28 as shownin FIG. 4. Optionally in embodiments the relative phase of the waveformsat inputs 5 and 23 is controllable to maximise the output from PSD block30.

In the embodiment of FIG. 9 the demodulated output is provided to ananalogue-to-digital converter 34 which provides an input to a processor33. Processor 33 controls the musical effects device and may optionallyprovide a user interface and/or display, for example to allow usersetting of the sensitivity, type of effect and the like, and to providecorresponding user feedback via a display. Thus processor 33 providesone or more digital control signals to a digital-to-analogue converter32 which in turn provides an analogue voltage or current level tocontrol the strength or other parameter of a musical effect applied byeffects block 35. The skilled person will be aware of many potentialeffects which may be applied including, but not limited to, wah-wah,fuzz and reverb. In one example the musical effects block 35 providesone or more controllable analogue filters, each filter beingconfigurable as a low-pass filter or a band-pass filter, each able tooperate independently under pedal control, optionally in combinationwith envelope control and/or a low frequency oscillator and/or a pitchtracking mode. Thus the user controls may include, for example, a modecontrol and a filter select control as well as a level control and,optionally, means for allowing the user to select a parameter to becontrolled by the pedal of the effects device. The musical effects block35 is coupled to a bypass switching block 38 which is in turn coupled toan audio input 36 and an audio output 37.

FIG. 10 shows a second embodiment of a musical effects device 200,illustrating a variant of the device of FIG. 9 in which the output 28 ofthe phase sensitive detector block 30 provides an analogue signal leveloutput which is used to directly control the musical effects block 35.Like elements to those of FIG. 9 are indicated by like referencenumerals.

FIG. 11 shows a third embodiment of a musical effects device 300, againin which like elements to those of FIG. 9 are indicated by likereference numerals. In the arrangements of FIG. 11 processor 33 providesa digital output to control musical effects block 35.

FIG. 12 a shows an example calibration procedure for the devices ofFIGS. 9 to 11. The procedure begins by measuring 120 the output voltageVmax at point 6 of the active circuit of FIG. 1 with maximum sensordisplacement. The procedure then measures 122 the output voltage at thispoint with minimum sensor displacement, Vmin, and then calculates 124 acalibration or scaling factor from these measurements. FIG. 12 b showsapplication of the calculated calibration/scaling factor duringoperation of the musical effects device: the output voltage at point 6is measured 126 and then processor 33 applies 128 the previouslydetermined calibration or scaling factor to the measured output voltageto calculate an output value for use in applying the musical effect.

In summary, we have described a non-contact sensor which can be used ina variety of ways to control aspects of a musical instrument's sound,whilst overcoming the deficiencies in previously developed sensors usedfor this purpose.

No doubt many other effective alternatives will occur to the skilledperson. Whereas the present invention has been described with respect tospecific embodiments thereof, it will be understood that the inventionis not limited to the described embodiments and encompassesmodifications apparent to those skilled in the art lying within thespirit and scope of the claims appended hereto.

We claim:
 1. A position sensor comprising an active tuned resonantcircuit, providing a signal which varies as the mutual separation ofsaid active tuned resonant circuit and an electrically reactive elementis varied, drive electronics connected to said active tuned resonantcircuit and read-out electronics connected to either said active tunedresonant circuit or said electrically reactive element.
 2. A positionsensor according to claim 1 wherein the electrically reactive elementhousing comprises a second, passive tuned resonant circuit, and furthercomprising: drive electronics coupled to said tuned resonant circuit todrive said first tuned resonant circuit with a drive signal at aresonant frequency; read-out electronics coupled to said first tunedresonant circuit, to provide a variable output signal responsive to saidrelative position of said second, passive tuned resonant circuit withrespect to first tuned resonant circuit, wherein a first frequency ofresonance of said firsts tuned resonant circuit matches a secondfrequency of resonance of said second, passive tuned circuit, andwherein said first and second frequency resonance match said resonantfrequency of said drive signal; wherein said first tuned resonantcircuit comprises an input coupled to said drive electronics, an outputcoupled to said read-out electronics and a resonant LC circuit coupledin series between said input and said output; and wherein said positionsensor is configured to provide a variable output signal is dependent onan amplitude of a signal at said output of said first tuned resonantcircuit.
 3. A position sensor according to claim 1 wherein theelectrically reactive element comprises a passive tuned resonantcircuit, or an electrically conductive object.
 4. A position sensoraccording to claim 1, wherein the mutual separation of the active tunedresonant circuit and the electrically reactive element is varied by amechanism or housing which directs the relative movement between saidactive tuned resonant circuit and said electrically reactive elementwhich allows the variation in said mutual separation to be linear,translational, angular or a combination of these.
 5. A position sensoraccording to claim 4 wherein the mechanism or housing comprises a footpedal, slider knob, or a rotary knob.
 6. A position sensor according toclaim 1, wherein the mutual separation of the active tuned resonantcircuit and the electrically reactive element is freely variable.
 7. Aposition sensor according to claim 6 wherein the active tuned resonantcircuit or the electrically reactive element is housed in a musicalinstrument or jewelry or clothing or baton or device moved by person orpersons involved in a musical performance.
 8. A position sensoraccording to claim 1 wherein the active tuned resonant circuit comprisesan inductive coil, at least one capacitive element and a means ofconnecting the drive electronics.
 9. A position sensor according toclaim 8 wherein the active tuned resonant circuit further comprises aninput resistor and at least two capacitive elements.
 10. A positionsensor according to claim 8 wherein the active tuned resonant circuitfurther comprises a means of connecting the read-out electronics to theinductive coil.
 11. A position sensor according to claim 3 wherein thepassive tuned resonant circuit comprises an inductive coil and acapacitive element.
 12. A position sensor according to claim 11 whereinthe passive tuned resonant circuit further comprises a means ofconnecting the read-out electronics.
 13. A position sensor according toclaim 8 wherein the inductive coils are formed from planar spiral trackson a printed circuit board.
 14. A position sensor according to claim 8wherein the inductive coils are wirewound.
 15. A position sensoraccording to claim 1 wherein the read-out electronics comprise asynchronous demodulation circuit, or a non-synchronous demodulationcircuit, or a phase-sensitive rectification circuit or aphase-insensitive rectification circuit.
 16. A position sensor accordingto claim 3 wherein the active tuned resonant circuit and the passivetuned resonant circuit are tuned to have the same frequency ofresonance.
 17. A position sensor according to claim 1, wherein saidsensor is usable as an electronic circuit element to directly control amusical effect signal.
 18. A position sensor according to claim 1,wherein the output from said sensor can be used to control a separatecircuit element in an musical effect electronic circuit or converted toa digital value via an analogue-to-digital-converter and used as aninput parameter to a digital signal processing algorithm or transmittedas musical instrument digital interface (MIDI) messages.
 19. A positionsensor according to claim 16 wherein a plurality of position sensors areoperated in close proximity where each position sensor operates at adifferent frequency of resonance.
 20. A position sensor according toclaim 16 wherein a plurality of position sensors are operated in closeproximity where each position sensor operates at the same frequency ofresonance.